Turbulent Dynamo Action in Binary Neutron Star Mergers

TL;DR

This study uses advanced simulations to demonstrate that turbulent dynamo processes during binary neutron star mergers can rapidly amplify magnetic fields, creating both small-scale turbulence and larger-scale magnetic coherence, impacting observable signals.

Contribution

First detailed general-relativistic MHD simulations showing the development of magnetic field amplification and large-scale coherence during neutron star mergers.

Findings

Rapid small-scale magnetic field growth indicating turbulent dynamo action

Emergence of large-scale coherent magnetic structures at high resolution

Implications for magnetic field strength and structure immediately after merger

Abstract

Binary neutron star mergers are expected to generate intense magnetic fields that power relativistic and non-relativistic outflows and shape their multimessenger signatures. These fields likely arise from the turbulent amplification of initially weak magnetic fields during the merger, particularly via the Kelvin-Helmholtz instability at the collisional interface between the stars. While previous studies have shown efficient amplification to magnetar-level strengths, the degree of large-scale coherence of the resulting field remains uncertain. We present general-relativistic, dynamical spacetime, magnetohydrodynamic simulations following the evolution of initially weak, pulsar-like magnetic fields in a binary neutron star merger. We find rapid magnetic field growth at small scales with clear signatures of small-scale turbulent dynamo action. At the highest resolutions, we additionally observe the emergence of coherent magnetic structures on larger scales. Our results imply that strong, ordered magnetic fields may be present immediately after merger, with important implications for the subsequent evolution of the remnant and its observable electromagnetic and gravitational-wave signals.